MicropumpsMicropumps can be grouped into mechanical and non-mechanical devices:[5] Mechanical systems contain moving parts, which are usually actuation and valve membranes or flaps. The driving force can be generated by utilizing piezoelectric, electrostatic, thermo-pneumatic, pneumatic or magnetic effects. Non-mechanical pumps function with electro-hydrodynamic, electro-osmotic, electrochemical [6] or ultrasonic flow generation, just to name a few of the actuation mechanisms that are currently studied.

Pioneering work on micropumps started in the 1970s and developments based on microfabrication technology was initiated in the 1980s. The MEMS based micropump was developed in 1990s. The micropump is the main component of drug delivery system that provides the actuation mechanism to deliver specific volumes of therapeutic agents/drugs from the reservoir. The requirements for drug delivery include a minimum flow rate in order of 10 L per minute or more, small size and high reliability [13]. Normally a micropump consists of the following components: diaphragm membrane, chamber, actuator, microchannels, microvalves, inlet, outlet, etc. Micropumps can be categorized into two classes: One type has a mechanical moving part and is known as a mechanical micropump; the other has no moving part and is known as a non-mechanical micropump.2.1. Design Specifications and Parameters of MicropumpsDesign of micropumps plays an important role for practical applications of devices. To develop a suitable design of micropumps for real time applications, it is very important to understand terms like actuator, valves, chamber or reservoir, nozzle diffuser mechanism and pumping parameters properly.2.1.1. ActuatorThe actuator is the necessary and driving part of a micropump that converts energy into motion. It is used to provide force for fluid flow in micropumps. The actuator takes energy from electricity, heat, liquid pressure, air pressure and converts it into some kind of motion. In most micropumps reported in literature, the actuation disk is attached with membrane which is used to push the fluid. Some types of time diaphragm are fabricated in such a way that it produces energy itself which pushes the fluid. In peristaltic micropumps more than one actuator is fabricated sequentially.2.1.2. ValvesIn micropumps, valves are used to control the fluid flow by opening, closing and partially hindering passageways. In microfluidic systems, active and passive valves have been reported. In passive valves there is no actuation mechanism. The control of fluid flow is dependent on the pressure difference in liquid chamber and the fluid flow is normally in one direction. In active valves, active elements are present for opening and closing that are operated by an external actuation source. Mostly, separate components have been reported for active micro-valves for regulating the fluid flow in microfluidic systems. It is very easy to control the active valves but they are more complicated in integrated microfluidic system.2.1.3. Chamber or ReservoirChamber design is very critical in microfluidic systems and it can significantly influence the volume stroke, pressure characteristics and nozzle-diffuser loss coefficients. Most of the micropumps reported in literature have a single chamber configuration. But in order to improve the performance, two or three chamber micropumps have also been reported. Micropumps in which pumping chambers are arranged sequentially or fabricated in such a way that the multiple chambers are in series or in parallel arrangements, are known as peristaltic micropumps.2.1.4. Nozzle/Diffuser ElementNozzle/diffuser element is mostly used in valveless micropumps as a flow rectifier. A schematic illustration of the nozzle/diffuser action in micropumps is shown in Figure 2. Nozzle/diffuser element works in such a way that during supply mode more fluid enters in the chamber through an inlet than fluid that exiting the outlet. While in pump mode the reverse action occurs. Stemme and Stemme [20] were the first to report valveless miniature micropumps in which they used a nozzle/diffuser element as flow rectifying element.The performance of mechanical micropump is normally limited by its mechanical components. The piezoelectric, electrostatic, thermopneumatic, electromagnetic, bimetallic, ion conductive polymer films (ICPF), phase change and shape memory alloy (SMA) are examples of mechanical micropumps. A detailed description of mechanical micropumps is given below.